Polymeric hydroxyalkyl terminated polysulphides as well as the preparation thereof have long been known.
Thus, U.S. Pat. No. 2,582,605 discloses a process where, for instance, bis-β-hydroxyethyl disulphide is condensed with itself or with other compounds having hydroxy groups such as glycols, in order to form corresponding polyethers. As catalyst, para-toluene sulphonic acid is mentioned.
Further, it is known from U.S. Pat. No. 4,124,645 that the preparation of such polymeric hydroxyalkyl terminated polysulphides apart from through polyether formation with itself or another polyether can be effected through the reaction of formaldehyde with the monomeric hydroxalkyl polysulphide.
The reaction described therein likewise is carried out in the presence of acid catalysts such as para-toluene sulphonic acid. Also in this process there is a question of a homogeneously catalytic reaction.
A disadvantage in this process is that the acid catalyst used has to be neutralized after completion of the reaction, e.g., para-toluene sulphonic acid with ammonia, as can be read in Example 1 of U.S. Pat. No. 4,124,645, so that the reaction mixture is not only freed of water and the optionally co-used solvents such as, e.g., benzene, but also the catalyst has to be separated off, since it could cause interference in further reactions and moreover is a drawback as an impurity.
It is a further disadvantage that it is not possible to obtain uniform products with the known process. In this respect, the hydroxylalkyl terminated polymeric polysulphides obtained according to the prior art leave something to be desired as regards the molecular weight distribution of the obtained polymers. For instance, the nonuniformity U is disproportionately high.
U is defined as
  U  =                    M        w                    M        n              -    1  
Also as a result of nonuniform polycondensation, molecules with a different structure are formed (block copolymeric structures).
However, for many application purposes, tailored products with a strictly alternating copolymer structure are desired, in particular when these polymeric polysulphides are not only put to use as such, but also should serve as starting products for the preparation of further functionalized polysulphides or for the preparation of polysulphides with a higher molecular weight.
Therefore, there is a need for polymeric hydroxylalkyl terminated polysulphides which stand out due to good properties, in particular as regards their polydispersity and structural uniformity, as well as for a corresponding preparation process.